Merge branch 'bpf-disable-preemption-in-perf_event_output-helpers-code'

Jiri Olsa says:

====================
bpf: Disable preemption in perf_event_output helpers code

hi,
we got report of kernel crash [1][3] within bpf_event_output helper.

The reason is the nesting protection code in bpf_event_output that expects
disabled preemption, which is not guaranteed for programs executed by
bpf_prog_run_array_cg.

I managed to reproduce on tracing side where we have the same problem
in bpf_perf_event_output. The reproducer [2] just creates busy uprobe
and call bpf_perf_event_output helper a lot.

v3 changes:
  - added acks and fixed 'Fixes' tag style [Hou Tao]
  - added Closes tag to patch 2

v2 changes:
  - I changed 'Fixes' commits to where I saw we switched from preempt_disable
    to migrate_disable, but I'm not completely sure about the patch 2, because
    it was tricky to find, would be nice if somebody could check on that

thanks,
jirka

[1] cilium/cilium#26756
[2] https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/commit/?h=bpf_output_fix_reproducer&id=8054dcc634121b884c7c331329d61d93351d03b5
[3] slack:
    [66194.378161] BUG: kernel NULL pointer dereference, address: 0000000000000001
    [66194.378324] #PF: supervisor instruction fetch in kernel mode
    [66194.378447] #PF: error_code(0x0010) - not-present page
    ...
    [66194.378692] Oops: 0010 [#1] PREEMPT SMP NOPTI
    ...
    [66194.380666]  <TASK>
    [66194.380775]  ? perf_output_sample+0x12a/0x9a0
    [66194.380902]  ? finish_task_switch.isra.0+0x81/0x280
    [66194.381024]  ? perf_event_output+0x66/0xa0
    [66194.381148]  ? bpf_event_output+0x13a/0x190
    [66194.381270]  ? bpf_event_output_data+0x22/0x40
    [66194.381391]  ? bpf_prog_dfc84bbde731b257_cil_sock4_connect+0x40a/0xacb
    [66194.381519]  ? xa_load+0x87/0xe0
    [66194.381635]  ? __cgroup_bpf_run_filter_sock_addr+0xc1/0x1a0
    [66194.381759]  ? release_sock+0x3e/0x90
    [66194.381876]  ? sk_setsockopt+0x1a1/0x12f0
    [66194.381996]  ? udp_pre_connect+0x36/0x50
    [66194.382114]  ? inet_dgram_connect+0x93/0xa0
    [66194.382233]  ? __sys_connect+0xb4/0xe0
    [66194.382353]  ? udp_setsockopt+0x27/0x40
    [66194.382470]  ? __pfx_udp_push_pending_frames+0x10/0x10
    [66194.382593]  ? __sys_setsockopt+0xdf/0x1a0
    [66194.382713]  ? __x64_sys_connect+0xf/0x20
    [66194.382832]  ? do_syscall_64+0x3a/0x90
    [66194.382949]  ? entry_SYSCALL_64_after_hwframe+0x72/0xdc
    [66194.383077]  </TASK>
---
====================

Link: https://lore.kernel.org/r/20230725084206.580930-1-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Alexei Starovoitov

kernel/trace/bpf_trace.c

@@ -661,16 +661,19 @@ static DEFINE_PER_CPU(int, bpf_trace_nest_level);
 BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map,
 	   u64, flags, void *, data, u64, size)
 {
-	struct bpf_trace_sample_data *sds = this_cpu_ptr(&bpf_trace_sds);
-	int nest_level = this_cpu_inc_return(bpf_trace_nest_level);
+	struct bpf_trace_sample_data *sds;
 	struct perf_raw_record raw = {
 		.frag = {
 			.size = size,
 			.data = data,
 		},
 	};
 	struct perf_sample_data *sd;
-	int err;
+	int nest_level, err;
+
+	preempt_disable();
+	sds = this_cpu_ptr(&bpf_trace_sds);
+	nest_level = this_cpu_inc_return(bpf_trace_nest_level);
 
 	if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(sds->sds))) {
 		err = -EBUSY;
@@ -688,9 +691,9 @@ BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map,
 	perf_sample_save_raw_data(sd, &raw);
 
 	err = __bpf_perf_event_output(regs, map, flags, sd);
-
 out:
 	this_cpu_dec(bpf_trace_nest_level);
+	preempt_enable();
 	return err;
 }
 
@@ -715,7 +718,6 @@ static DEFINE_PER_CPU(struct bpf_trace_sample_data, bpf_misc_sds);
 u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
 		     void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy)
 {
-	int nest_level = this_cpu_inc_return(bpf_event_output_nest_level);
 	struct perf_raw_frag frag = {
 		.copy		= ctx_copy,
 		.size		= ctx_size,
@@ -732,8 +734,12 @@ u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
 	};
 	struct perf_sample_data *sd;
 	struct pt_regs *regs;
+	int nest_level;
 	u64 ret;
 
+	preempt_disable();
+	nest_level = this_cpu_inc_return(bpf_event_output_nest_level);
+
 	if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bpf_misc_sds.sds))) {
 		ret = -EBUSY;
 		goto out;
@@ -748,6 +754,7 @@ u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
 	ret = __bpf_perf_event_output(regs, map, flags, sd);
 out:
 	this_cpu_dec(bpf_event_output_nest_level);
+	preempt_enable();
 	return ret;
 }